Over the past few months, I have been working with many different types of charities, from campaigning groups to local counselling charities - and all of them have raised the thorny question of how to demonstrate the impact of what they do.

They are not alone. Around the country, managers in charities and the public sector are trying to demonstrate the value of their work and prove it is effective. A few are happy with where they are; most are struggling. Almost without exception, this work is being done in isolation.

Measuring Family Ties, published today by New Philanthropy Capital, funded by the Indigo Trust, is the first in a series of projects working collaboratively with a group of charities to develop standard ways to measure their impact - a common measurement framework.

The report looks at how charities who aim to maintain and improve relationships between prisoners and their families can demonstrate the value of their work. This is a challenging area. The outcomes are largely intangible, the government does not collect or share much data, and there is a lack of money and tools available for evaluation.

These issues are common in the third sector and we believe other charities could benefit from working together to develop, test and use standard approaches to measuring their impact.

We worked with six charities: Action for Prisoners' Families, Kids VIP, Pact, POPS, Safe Ground and Storybook Dads.

Our starting point was to map how all the different activities carried out by the charities contribute to improving family relationships. It can be very difficult for charities to explain why any single activity is important because changing family relationships is so complex. Mapping these activities provides charities and funders with a clear and agreed understanding of this.

It also shows what change charities can expect to achieve, and so what it is reasonable to measure. On its own, running a visitor centre is not going to strengthen family relationships, but it should make the experience easier for the family, enabling them to have a better conversation with the prisoner and perhaps even encouraging them to visit more often.

We also had to tackle the all-important question: "How can we show we are doing a good job?" Two priority areas emerged: the experience of prison visitors and the strength of prisoners' family relationships. Together with the charities, we developed and piloted two questionnaires designed to capture changes in these areas.

The results were useful; they showed that 84% of people agreed the visitors' centre helped make the visit as stress-free as possible, and that using drama and group work significantly improved the relationship from the perspective of the prisoners' family members. The pilots were limited, but convinced all involved of the value of the approach.

It wasn't all smooth running. Co-ordinating six organisations inevitably brings challenges. At times the strain of working collaboratively in a competitive environment for government contracts and other sources of funding became clear. And time and capacity is always in short supply. But we managed it and the fact that there is enthusiasm to continue to use the tools is testament to its success.

The potential of this approach is really exciting. At the most basic, it helps charities to measure results better. It also helps charities to communicate with funders or commissioners, by identifying what is reasonable to measure.

Perhaps best of all, it is the first step towards developing standard approaches to good quality measurement, reducing wasted effort and duplication, and ultimately allowing charities and funders to understand the effectiveness of different approaches.